Insulin resistance is a hallmark of type 2 diabetes mellitus. The prevalence of insulin resistance and diabetes is increasing at an alarming rate, in part, because of a rapid increase in obesity in all populations. The goals of the proposed program are to (a) further our understanding of obesity-associated insulin resistance, and (b) prepare the PI for an independent research career. We will approach the research questions by creating and studying mouse models in which triglyceride synthesis is increased in only adipose tissue or only muscle. Two transgenic mouse models with tissue-specific overexpression of diacylglycerol acyl transferase (DGAT) will be studied. DGAT is a key enzyme in triglyceride (TG) synthesis. Overexpression of this enzyme in cells leads to increased intracellular fat accumulation. Mouse models with DGAT overexpression will enable the PI to closely examine if and how insulin resistance develops secondary to a primary increase in triglyceride synthesis in each tissue. By separately and specifically introducing a DGAT transgene into the mouse?s adipose tissue and muscle, to increase fat content in the respective tissues, these mouse models will enable the investigators to better dissect the usually complex processes involving multiple tissues and organ systems in the interaction between obesity and insulin resistance. The Specific Aims of this project are to answer the following two fundamental questions involved in this relationship: (1) whether simple obesity caused by an increased capacity of TG synthesis in adipose tissue can alter plasma lipid and/or hormone and cytokine levels, eventually leading to insulin resistance, (2) whether enhanced TG deposition in muscle alone is sufficient to cause muscle and systemic insulin resistance. This project will be conducted at Columbia University College of Physicians and Surgeons in a highly enriched research environment, particularly with respect to lipid metabolism and diabetes research. The PI has had previous basic science training in cell biology, and more recent training in internal medicine and clinical endocrinology. The proposed research will be performed under the mentorship of Dr. Henry Ginsberg, who has a long and outstanding record in research involving both diabetes and lipoprotein metabolism. The mentor also has extensive training experience. Additionally, as part of the program, the PI will acquire new research skills, including the performance of lipoprotein turnover studies and insulin clamps in transgenic mice, and the use of microarray gene expression methods. Related formal course work will also be included in the overall program. The establishment and studies of the two transgenic mouse models, together with the specific technologies he will acquire during the course of this project, will provide the PI with an outstanding base from which to launch a career as an independent translational research scientist.